Abstracts

Rationale: Multiple hippocampal transection (MHT) and multiple subpial (cortical) transection (MST) are transective surgeries to treat epilepsy. In these surgeries seizure circuits are disrupted by transection of horizontal interneuronaI fibers. In addition, function is preserved because tissue is not removed and fibers responsible for function (which are vertical fibers) are preserved. In this paper the benefit of intraoperative ECoG during transective surgeries for temporal lobe epilepsy is prospectively examined. Methods: Fourteen patients who have a follow-up of at least one year, have unilateral temporal lobe seizures and had intraoperative electrocorticography (ECoG) during their surgeries are included in this report. The follow-up is between 12-48 months with a median of 26 months. The ages of the patients were between 20-48 years. The male female ratio is 8/6. Routine preoperative evaluation, including neuropsychological evaluation and ECoG using subdural and depth electrodes were done. All patients had MST over the neocortex and MHT on the hippocampus. MHT was done through the middle temporal gyrus and the temporal horn. Transverse cuts were made through the length of the hippocampus at 4 mm interval. The fimbria however was left intact. Amygdalectomy was done if seizure focus was present in the amygdala (9 patients). The entorhinal cortex was left intact. Intra operative ECoG was then done. If recordings showed areas of persistant epileptogenic activity, transections were repeated over the area of the activity. If this activity persisted after second pass, the innvolved cortex was resected. The hippocampus, however, was never resected. Results: Based on intraoperative ECoG repeat transection was needed in every case; though the second pass was over a much smaller area. Resection of neocortex (measuring 1-2.5 cm in diameter) was needed in 10 patients. This was always around the temporal tip. There were no permanent neurological complications. Twelve patients (85.7%) are Seizure free (Engels' Class I) and 2 (14.3%) have rare seizures (Class II). Neuropsychological studies showed that verbal memory was preserved.Conclusions: Transective surgeries may not necessarily eliminate epileptogenic activity in all areas of the temporal lobe. Therefore, to detect residual areas with epileptogenic activity, intraoperative ECoG is critical. Furthermore, some areas may need resection because epileptogenic activity in them may persist even after a second MST pass. Fortunately the areas needing resection were very small. Though the series is small and the follow-up is relatively short, the results are encouraging because the seizure control achieved is comparable to those obtained by standard temporal lobectomy. Furthermore, the hippocampus, which is the main source of stem cells is preserved; and verbal memeory was left intact. Therefore, this may be a good approach for those patients who are are at a higher risk for memory impairment with a standard temporal lobectomy procedure.